Oxidation process

ABSTRACT

MANUFACTURE OF AN ALKANE DICARBOXYLIC ACID, PARTICULARLY ADIPIC ACID BY FEEDING AN ALKANOL, ALKANONE OR MIXTURE INTO NITRIC ACID OF 40-70% (PREFERABLY 50-65% STRENGTH AND FRACTIONALLY DISTILLING VOLATILE MATTER FROM THE OXIDATION ZONE TO KEEP UP THE STRENGTH OF THE NITRIC ACID AND THEREBY IMPROVE THE YIELD OF DICARBOXYLIC ACID.

United States Patent 1 OXIDATION PROCESS Frank Leach Foster and PeterHay, Manchester, England, assignors to Imperial Chemical IndustriesLimited, London, England No Drawing. Filed Feb. 4, 1971, Ser. No.112,760 Int. Cl. C07c 55/14, 55/04 US. Cl. 260-531 R 9 Claims ABSTRACTOF THE DISCLOSURE Manufacture of an alkane dicarboxylic acid,particularly adipic acid by .feeding an alkanol, alkanone or mixtureinto nitric acid of 40-70% (preferably 50-65%) strength and fractionallydistilling volatile matter from the oxidation zone to keep up thestrength of the nitric acid and thereby improve the yield ofdicarboxylic acid.

This invention relates to a process for the oxidation of cycloalkanolsand/or cycloalkanones to produce alkane dicarboxylic acids, and inparticular of cyclohexanol and/ or cyclohexanone to produce adipic acid.

It is known to manufacture adipic acid by oxidising with nitric acid amixture of cyclohexanol and cyclohexanone commonly called KA (ketone/alcohol) which is obtained by oxidising cyclohexane with anoxygen-containing gas such as air. Catalysts, for example copper andvanadium salts have an advantageous efiect on this oxidation. During thenitric acid oxidation the concentration of nitric acid and catalystfalls, partly because water is formed and partly because some of thenitric acid is used up. Even in continuously operated processes theconcentration of nitric acid does not remain constant throughout theoxidation zone, being lower in the vicinity of the exit than it is atthe entry. In known processes the practice has been to recover nitricacid after isolation of adipic acid and byproducts therefrom and then toconcentrate the recovered nitric acid by fractionation before re-usingit in the oxidation process.

According to the invention a process for the manufacture of an alkanedicarboxylic acid comprises oxidising an initail material consisting ofa cycloalkanol and/or a cycloalkanone by feeding the same into nitricacid in an oxidation zone, the nitric acid supplied to the oxidationzone being of 40 to 70% strength by weight, the temperature being theapparent boiling point (as hereinafter defined) of the mixture at theoperating pressure and the rate of feed being such that distillationtakes place through a fractionation zone and reduction of nitric acidstrength in the oxidation zone is thereby lessened.

Examples of initial material to be used in the process arecyclopentanol, cyclohexanol, cyclohexanone, methylcyclohexanol,methylcyclohexanone, cyclooctanol, cyclo dodecanol, cyclododecanone, andmixtures of these. The preferred initial material is thecyclohexanol/cyclohexanone mixture known as KA since this producesadipic acid, a valuable intermediate for the manufacture of nylon 6.6(polyhexamethyleneadipamide).

By apparent boiling point we mean the temperature at which ebullitiontakes place with the production of a refluxing stream of aqueous nitricacid. This temperature is lower than true boiling point of the nitricacid in the oxidation zone since bubbles of oxides of nitrogen areformed by the oxidation.

Although the nitric acid supplied to the oxidation zone is of 40 to 70%strength by weight (preferably 50 to 65% by weight) the nitric acidstrength within the oxidation zone (defined as weight of nitricacidXIOO/Weight of nitric acid plus water) will be less than this exceptduring start up. Preferably however the mean nitric acid strength p CCwithin the oxidation zone should not fall below 40%. To obtain greatestadvantage from the invention the rate of distillation should be suchthat the mean nitric acid strength within the oxidation zone should besubstantially equal to that of the nitric acid supplied thereto.

For batch-wise operation of the process it is convenient to feed theinitial material to be oxidised into a large excess of nitric acid of 40to 70% (preferably 50 to 65%) strength by weight adding more nitric acidif necessary as the oxidation proceeds.

For continuous operation the initial material and nitric acid may be fedsimultaneously into an oxidation zone. For best results incoming nitricacid should become thoroughly mixed with mixture already in theoxidation zone before it meets incoming initial material. This can beaccomplished either by eflicient stirring or by cycling material fromthe oxidation zone into the incoming nitric acid.

The pressure in the oxidation zone may be atmospheric or less than this,preferred operating pressures being such that the apparent boiling pointof the mixture in the oxidation zone is 70 to C. Such pressures are inthe region of -200 mm. Hg.

Any catalyst used in the process, particularly copper and vanadium saltsmay be fed into the oxidation zone in solution in the nitric acid.

After carrying out the process of the invention the product may beworked up in known manner. Thus for example the mixture leaving theoxidation zone may be freed from nitrous fumes by contact with an inertgas e.g. air, or nitrogen and the nitrous fumes, together if desiredwith those which are evolved during the oxidation may be converted intonitric acid for example by absorption in distillate produced in theprocess, thereby providing a step in the recovery of nitric acidsuitable for re-use in the process. Alkane dicarboxylic acids may beseparated by crystallisation of the liquors after freeing from nitrousfumes, and mother liquors may be concentrated to recover furtherquantities if desired. Dilute nitric acid streams recovered during thework up may be concentrated as in prior art processes but the cost ofsuch concentration is reduced because of the utilisation of reactionheat for fractionation purposes during the oxidation process itself.

Yields of alkane dicarboxylic acids produced by the process of theinvention are superior to those obtainable by comparable prior artprocesses in which no fractional distillation of nitric acid is carriedout. In particular the process gives higher yields of adipic acid fromcyclohexanol/cyclohexanone (KA) mixtures than are obtainable by theprior art methods. Moreover the adipic acid is accompanied by smallertotal proportions of other dicarboxylic acids, particularly glutaric andsuccinic acids, than are produced by the prior art methods, so that agreater proportion of the adipic acid is readily recoverable byestablished methods of crystallisation.

It is a further advantage of the process of the invention that thedissipation of reaction heat through the fractionation reduces thenecessity for external cooling of the reaction zone and may be used toprovide an effective means of temperature control.

The invention is illustrated but not limited by the following Examples1, 3 and 5 in which all percentages are by weight. Examples 2, 4 and 6are comparative examples.

EXAMPLE 1 The apparatus employed consisted of a 1 l. flask with 3 necksinto which were fitted:

(a) a glass link stirrer rotating at approx. 600 rpm. (b) a. droppingfunnel containing the charge of cyclohexanol/cyclohexanone (c) athermometer and a lagged Vigreux column (360 mm. etfective length)leading to a condenser set for distillation into a suitable receiver.

The flask was heated with an electric heating mantle.

Nitric acid containing copper and vanadium catalyst (441 g. actualweight containing 50% HNO 0.2% copper added as copper metal, and 0.02%vanadium added as ammonium metavanadate) was charged to the flask andheated to the boiling point of approx. 115 C. using the electric heaterand allowed to reflux in the Vigreux column in order to warm up thecolumn. Dropwise addition of a cyclohexanol/cyclohexanone mixture wasthen started. There was an immediate reaction, as shown by the evolutionof oxides of nitrogen, and distillation took place from the reactor intothe receiver. By suitable adjustment of the electricity supply to theheater and of the rate of addition of the cyclohexanol/cyclohexanonemixture distillation was maintained throughout the reaction temperatureof approx. 110 C. Addition of the cyclehexanol/cyclohexanone mixture(60.15 g. actual weight containing 13.68% water i.e. 51.92 g. dryweightthe cyclohexanolzcyclohexanone ratio of the mixture was approx.9:1) took place over approximately /2 hr. The reaction mixture wasallowed to cool, with stirring, over about an hour and subsequentlycooled in an ice/water bath and stirred for a further hour at about C.The precipitated adipic acid was filtered off and washed with 140 cc. oficed water. The filter cake was dried overnight at 110 C. to yield adried product weighing 59.95 g. The combined filtrate and wash samplewas analysed for nitric acid by titration and for adipic, glutaric andsuccinic acids by Gas Liquid Chromatography of the dimethyl esters. Thedistillates, which amounted to 139 g. was similarly analysed.

The total yields of dibasic acids obtained from the filter cake and thecombined filtrate and wash sample were: 123.7 g. adipic acid, 10.3 g.glutaric acid and 3.1 g. succinic acid per 100 g. of drycyclohexanol/cyclohexanone mixture. In addition a further 0.2 g. adipicacid per 100 g. dry cyclohexanol/cyclohexanone mixture was found in thedistillate sample.

From the nitric acid analyses it was shown that the nitric acid strength(as hereinbefore defined) in the reaction mixture at the conclusion ofthe reaction was 42.4%. The distillate contained 36.3 g. of nitric acidand 102.4 g. Water.

The cyclohexanol/cyclohexanone mixture used in this example was obtainedby oxidation of cyclohexane with air.

Similar results are obtained by oxidising pure cyclohexanol or purecyclohexanone under the conditions described in this example.

EXAMPLE 2 (Comparative) A control experiment in which the conditionswere identical with Example 1 except that the Vigreux column/distillation assembly was repiaced by a reflux condenser, was carriedout using the same cyclohexanol/cyclohexanone mixture. (59.88 g. actualwt.:51.69 g. dry wt.).

The dibasic acid yields were 122.4 g. adipic acid, 11.3 g. glutaric acidand 3.1 g. succinic acid per 100 g. of dry cyclohexanol/cyclohexanone.

From the nitric acid analyses the nitric acid strength of the reactionmixture at the conclusion of the reaction was 35.4%.

EXAMPLE 3 A further experiment was carried out in a similar manner tothat of Example 1 except that the pressure was maintained at 140-200 mm.(absolute) and boiling occurred at 78-83.5 C. The amount ofcyclohexanol/ cyclohexanone mixture used was 59.14 g. actual weight(51.05 g. dry weight) and the yields of dibastc acids were 130.0 g.adipic acid; 7.2 g. glutaric acid; and 2.3 g. succinic acid per 100 g.dry cyclohexanol/cyclohexanone mixture. A further 0.1 g. adipic acid perg. dry cyclohexanol/cyclohexanone mixture was found in the distillate.

The nitric acid analysis showed that the nitric acid strength (asdefined above in Example 1) at the conclusion of the reaction was 56.9%.The distillate contained 34.8 g. nitric acid and 148 g. water.

EXAMPLE 4 (Comparative) A control experiment was carried out undersimilar conditions of temperature and pressure to those used in Example3 except that the distillation assembly was replaced by a refluxcondenser. In this case 59.61 g. actual weight (51.46 g. dry weight) ofcyclohexanol/cyclohexanone mixture yielded 124.5 g. adipic acid; 8.8 g.glutaric acid; and 3.7 g. succinic acid per 100 g. dry cyclohexanol/cyclohexanone mixture. The nitric acid strength at the conclusion of thereaction was 37.1%.

EXAMPLE 5 The apparatus used in this example was designed to simulatethe operation of a stirred tank continuous reactor. It consisted of a 21spherical vessel set in an electric heating mantle and fitted with aVigreux fractionating column and condenser as described in Example 1,and with a flat stainless steel paddle agitator (7.5 x 2.0 cm.) whichwas rotated at approx. 100-200 r.p.m. During the course of the reactionthe cyclohexanol/cyclohexanone mixture (*KA) was continuously pumpedinto the reactor via a in. (outside diameter) stainless steel capillarytube which discharged at a point below the axis of the stirrer, and thenitric acid required was continuously pumped in via a /8 in. (outsidediameter) tube discharging at the side wall of the reactor. The amountof cyclohexanol/ cyclohexanone used was measured by weighing, and theamount of nitric acid by volume. The reactants were metered into thereactor using a plunger type metering pump. The temperature of thereactor liquid was measured and recorded using a stainless steelsheathed thermocouple connected to a suitable recorder. The reactor,distillate receiver and the cyclohexanol/cyclohexanone and nitric acidreservoirs were connected to a vacuum manifold so that the pressure ofthe system could be held at any desired value from about 100 mm. toatmospheric pressure by use of a suitable manostat.

Before commencing the reaction the reactor was charged with 200 ml. of anitric acid solution containing 50.3% nitric acid, 0.2% copper and 0.02%vanadium. The pressure of the system was set at -170 mm. Hg and the acidwas heated to boiling point to warm up the Vigreux fractionating column.Simultaneous addition of the cyclohexanol/cyclohexanone mixture and ofthe nitric acid solution (of the same strength and metal content as thatused for the initial charge) was then commenced. There was an immediatereaction, as shown by the evolution of oxides of nitrogen, anddistillation took place into the distillate receiver. The temperature ofthe reaction medium was 77-79 C. throughout the addition, which wasterminated when the reactor became substantially fill. The reactionmixture was subsequently worked up as described in Example 1. Details ofthe weight of cyclohexanol/cyclohexanone charged, the operatingconditions, the distillate, the nitric acid strength (as hereinbeforedefined) of the terminal reaction product, and the yields of adipic,glutaric and succinic acids are shown in the table which follows Example7.

EXAMPLE 6 (Comparative) To ascertain the result obtained when there isno distillation to maintain acid strength during reaction, the procedureof Example 5 was repeated under reflux conditions. The starting chargeof nitric acid consisted of 200 ml. of a nitric acid solution containing40.4% nitric acid together with 0.2% copper and 0.02% vanadium in orderto simulate the conditions of a stirred tank continuous reactor duringoperation. The nitric acid added 3,754,024 during the reaction was ofthe same strength as used in strength within the oxidation zone and toinsure that the Example 5, i.e. 50.3%. The temperature of the reactionnitric acid strength does not fall below 40%, the rate of was 74-75 C.Experimental details are shown in the distillation being such that themean nitric acid strength table. It may be seen that the yield of adipicacid, and within the oxidation zone is at least substantially equal theterminal reaction product nitric acid strength are ap- 5 to that of thenitric supplied thereto.

preciably lower than when distillation was employed dur- 2. Processaccording to claim 1 wherein the nitric acid ing the reaction. suppliedto the oxidation zone is of 50 to 65% strength.

EXAMPLE 7 (Cbmpamtive) 3. Process according to claim 1 wherein thecyclohexanol and cyclohexanone are obtained by oxidising In this examplethe precedure of Example 6 was re- 10 cyclohexane with anoxygen-containing gas.

peated at atmospheric pressure, i.e. without concentra- 4. Processaccording to claim 1 operated continuously tion and without boiling,which is the conventional way of by feeding initial material and nitricacid simultaneously conducting the reaction. The temperature was withinthe into an oxidation zone, the said nitric acid becoming range 78.579.5 C. during the addition. In order to con thoroughly mixed withmixture already in the oxidation trol the temperature in the experimentthe electric heatzone before it meets incoming initial material. ingmantle was replaced by a water bath held at about 5. Process accordingto claim 1 operated continuously 70 C. As may be seen from the resultsin the table the by feeding initial material and nitric acidsimultaneously yield is greater than for the vacuum reflux Example 6into an oxidation zone, the said nitric acid becoming but is stillsignificantly less than for the distillation/conthoroughly mixed withmixture already in the oxidation centration experiment (Example 5). zonebefore it meets incoming initial material.

TABLE Yield dibasic acids Nitric (grams per 100 g. dry

acid Duracyclohexanol/cyclo- Terminal Distillate Weight 01 (mol/ tionhexanone mixture) nitric KA (grams) moll) Pressure of acid Total WeightWeight oiKA range, run Glu- Sucstrength, weight HNOs H20 Ex. No. Mode ofoperation Wet Dry charged mm. Hg. (111111.) Adipic taric cinic percentgram gram gram Vacuum distillation--- 192.53 176.11 8.6 160-168 117131.5 7.7 1.1 50.2 669.4 125.2 544.2

Vacuumrefiux 117.97 110.04 8.3 163-165 14 124.2 9.8 3.4 .0 Atmosphericressure 118.65 110.68 7.0 67 127.9 7.3 2.5

(not 1101111115.

1 This figure relates to the amount of acid pumped in during thereaction period and does not include the starting charge.KA=cyclohexanoll cyclohexanone mixture.

2 As hereinbeiere defined.

! Atmos. pressure.

Comparing Examples 6 and 7 it may be seen that oxi- 6. Process accordingto claim 1 operated at a pressure dation at low pressure is not initself beneficial, since the such that the apparent boiling point of themixture in the yield of adipic acid produced is diminished. Comparingoxidation zone is 70 to 85 C.

all these three examples however it is to be seen that 7, Processaccording to claim 1 operated at a pressure the fractional distillationused in Example 5 outweighs such that the apparent boiling point of themixture in the the eifect of the low pressure operation and in factprooxidation zone is 70 to 85 C.

dIlCBS a higher adipic acid Yifiid than that Obtained 8. Processaccording to claim 4 operated at a pressure ample at the Sametemperature under atmospherlc such that the apparent boiling point ofthe mixture in the pressure. oxidation zone is 70 to 85 C.

Using 65% nitric acid instead of the 50.3% n tric 9. Process accordingto claim 5 operated at a pressure acid used i EXamPIeS 6 and 7 theyleld? 0f P F such that the apparent boiling point of the mixture in theacid are all increased, but the same comparative eifect 1s Oxidationzone is 70 to 35 seen, the fractional distillation outweighing thenon-beneficial effect of low pressure operation, and producing aReferences Cited higher yield than that obtained at the same temperatureunder atmospheric pressure. UNITED STATES PATENTS We claim: 2,719,1729/1955 Nebe et a1. 260-531 R 1. A process for the manufacture of analkane dicar- 3,290,367 12/1966 White et a1. 260531 R boxylic acidcomprising supplying nitric acid of 40 to 70% strength by weight to anoxidation zone, feeding FOREIGN PATENTS into the oxidation zone amixture consisting essentially of 1,280,340 10/1968 Germany 260-431 R cclohexanol and c clohcxanone, the temperature in the oxidation zone beirig the apparent boiling point of the LORRAINE WEINBERGER Pnmary Exammermixture of substances therein, and distilling volatile ma- R. D, KELLY,A i t t E i terial through a fractionation zone at a rate controlled bythe feed rate of the cyclohexanol/cyclohexanone mix- US. Cl. X.R.

ture whereby to lessen the reduction of nitric acid 260-537 P Patent No.3, 754, 024

Inventor(:;)

Dat Auqust 21. 1973 Frank Leach Foster and Peter Hay It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 9, insert -Claims priority, application Great BritainFebruary 14, 1970, 1834/70 Signed and sealed this 25th day of December1973.

(SEAL) Attest:

EDWARD M.ELETCHER,JR. Attesting Officer RENE D. TEGTMEYER ActingCommissioner of Patents

